Rescue workers struggled to reach ravaged towns and villages in the central Philippines on Monday while soldiers tried to quell looting in the chaotic aftermath of a powerful typhoon that killed an estimated 10,000 people and displaced more than 600,000.

The United Nations said some survivors had no food, water or medicine, and that local officials had reported a mass grave of 300-500 bodies in the devastated city of Tacloban. Relief operations were hampered because roads, airports and bridges had been destroyed or were covered in wreckage, it said.

Threatening to worsen the crisis in the impoverished area, a tropical depression carrying heavy rain was forecast to arrive in the region early on Tuesday.

President Benigno Aquino, facing one of the biggest challenges of his three-year rule, deployed soldiers to Tacloban to restore order and said he might impose martial law or a state of emergency.

But three days after it was hit by one of the strongest typhoons on record, the city of 220,000 residents was still relying almost entirely for supplies and evacuation on just three military transport planes flying from nearby Cebu city.

"I lost my house, I lost everything. I want to get out. My food supply will run out in two days," said Maria Elnos, a nurse at Tacloban's one main hospital, who was among hundreds pleading unsuccessfully to get on a military C-130 plane late on Sunday.

Super typhoon Haiyan is estimated to have destroyed about 70 to 80 percent of structures in its path as it tore into the coastal provinces of Leyte and Samar on Friday. Most of the damage and deaths were caused by huge waves that inundated towns and swept away coastal villages in scenes that officials likened to the 2004 Indian Ocean tsunami.

DEATH TOLL COULD CLIMB

The Philippines government and disaster agency have not confirmed the latest estimate of the number of deaths from the storm, whose sustained winds reached 195 miles per hour (313 km per hour) with gusts of up to 235 mph (378 kph).

Police chief superintendent Elmer Soria, quoting local officials, said the estimated death toll so far was 10,000. That could climb once rescuers reach remote villages along the coast, such as Guiuan, a town in eastern Samar province with a population of 40,000 that was largely destroyed.

Images from an armed forces flight over the town showed apocalyptic scenes, with survivors wandering dazed among the shells of shattered buildings and splintered trees. No relief supplies have reached the remote town.

"The only reason why we have no reports of casualties up to now is that communications systems ... are down," said Colonel John Sanchez, posting on the Armed Forces Facebook page.

Terminal buildings at the Tacloban airport were largely destroyed although the runway was still operational.

About 300 people died in Samar province, said an official from the provincial disaster agency.

Baco, a city of 35,000 in Oriental Mindoro province, was 80 percent under water, the U.N. said.

Nearly 620,000 people were displaced and 9.5 million "affected" across nine regions, the U.N.'s Office for the Coordination of Humanitarian Affairs (OCHA) said in a statement.

Across Tacloban, men, women and children walked carefully over the remains of wooden houses, searching for missing loved ones and belongings. Not one building seems to have escaped damage in the coastal city, about 580 km (360 miles) southeast of Manila.

Witnesses and officials described chaotic scenes. The city and nearby villages were flooded, leaving floating bodies and roads choked with debris from fallen trees, tangled power lines and flattened homes.

Survivors queued in lines, waiting for handouts of rice and water. Some sat and stared, covering their faces with rags to keep out the smell of the dead from one of the worst disasters to hit the typhoon-prone Southeast Asian nation.

One woman, eight months pregnant, described through tears how her 11 family members had vanished, including two daughters. "I can't think right now," she said. "I am overwhelmed."

U.S. MARINES ON WAY

About 90 U.S. Marines and sailors headed to the Philippines in a first wave of promised military assistance for relief efforts, U.S. officials said. President Barack Obama said the United States was ready to provide additional aid.

U.S. aid groups also launched a multimillion-dollar relief campaign. One group, World Vision, said a shipment of blankets and plastic tarpaulins would arrive from Germany on Monday as a first step in its plan to help 400,000 people.

An official of World Vision based in Cebu Province said there were early reports that as much as 90 percent of northern Cebu had been destroyed.

An aid team from Oxfam reported "utter destruction" in the northern-most tip of Cebu, the charity said.

The United Nations children's agency, UNICEF, said it was rushing emergency supplies to the Philippines.

AQUINO SENDS IN TROOPS

Aquino said the government had deployed 300 soldiers and police to restore order in Tacloban.

Looters rampaged through several stores in the city, witnesses said. A TV station said ATM machines were broken open.

Thirteen people were killed and dozens hurt during heavy winds and storms in Vietnam as Haiyan approached the coast, state media reported, even though it had weakened substantially after hitting the Philippines.

Vietnam authorities have moved 883,000 people in 11 central provinces to safe zones, according to the government's website. A further 150,000 people were moved to safe areas in northern provinces, authorities said.